An important consideration in the design of high technology equipment is the ease of service and maintenance of the equipment once it is placed in its operational environment. Therefore, almost without exception all equipment involving complex electronic circuitry utilize modular construction techniques wherein much of the circuitry whether purely electronic or various hybrids thereof comprise printed circuit boards mounted in card cages. The card cages which may be integral parts of the equipment to be controlled contain a plurality of printed circuit boards. The printed circuit boards are easily removed from the card cages for servicing. In most cases the serviceman may simply replace the defective circuit board with a new one and return the defective one for repair at a service center. Thus, the equipment is serviceable with a minimum of down time.
A disadvantage of such construction is that each printed circuit board contains completely different circuitry from the other cards in the cage and must be replaced with one that is identical.